The present invention relates generally to structural monitoring systems, and more particularly to monitoring systems embedded within a structure that includes autonomous power supplies, sensors, and wireless communication.
Structural monitoring is a known field used to examine the integrity of structures and predict when maintenance activities should be performed. Most conventional prior art in this field pertains to sensor systems which use sensors that are wired to a central data acquisition and processing unit. Structural monitoring systems have been applied historically in situations where the cost to benefit ratio is low, because the sensor systems add significant cost, additional maintenance requirements, and a level of reliability that may not coincide with that of the structural system being monitored. For example, health monitoring sensors in power plants are often used because common failures cost millions of dollars in down time, while bridge monitoring sensors are not typically employed because bridges rarely fail and sensor installations are costly. The cost-benefit ratio for each application depends on both the cost savings that can be derived from early failure prediction and the lifecycle cost of the particular implementations of the structural monitoring system. The lifecycle cost for most monitoring systems is in large part determined by the wired connections between remote sensor locations and a central data acquisition and processing unit. Wiring faults are common and are often difficult to diagnose, which increases the maintenance required to sustain the monitoring system. Wire installation costs are high because the wire often needs to be protected.
In addition to wiring, the typical external mounting and means of attachment of a monitoring device to a structure strongly influences their accuracy, performance stability and ultimately lifecycle cost of such devices. Small degradation in adhesives or mechanical fastener boundary conditions due to corrosion leads to changes in the operation of sensor and power supply, which can radically compromise the value that they offer. Changes to the sensor mount may require recalibration of device, which erodes the maintenance reduction objectives of the monitoring system. Changes to the power supply mount can affect output, which compromises the performance of the whole monitoring system. External mounting of sensor systems presents further drawbacks in terms of vulnerability to external damage or tampering.
In the specific case of helicopter components such as rod ends, replacement is often initiated by the appearance of damage and blemishes in the external surface of the structural part. These blemishes may result from impacts with small debris during operation or from maintenance activities in the proximity of the structural part. Considering the robustness of metal components relative to the vulnerability of an externally mounted device of a monitoring system, there is an issue of whether the devices of the monitoring system must be replaced more often than the structure that is being monitored.
A common problem with prior load sensors such as wire foil strain gauges is induced noise from external electromagnetic sources. Foil strain gauges can behave similar to an antenna, because they are typically exposed and mounted to a metal component. This is a particularly relevant issue in structural monitoring systems, if wireless communication and wireless power transfer is used.
It is an object of the present invention to provide a structural monitoring system which can be embedded in a structure.
It is an object of the present invention to provide a structural monitoring system which does not require wired connections for power or communication.
It is an object of the present invention to provide a structural monitoring system with improved system robustness and reduced susceptibility to tampering.
It is an object of the present invention to provide a structural monitoring system with reduced maintenance and improved useful life of the monitoring system.